The definition of evolution is itself part of the controversy over evolution. There are several meanings in common use.

Change in the history of the universe. This includes biological change, and non-biological change, such as galaxy formation. When evolutionist Theodosius Dobzhansky (1900-1975) said, "Nothing in biology makes sense except in the light of evolution",[1] he meant that "Evolution comprises all the stages of the development of the universe: the cosmic, biological, and human or cultural developments. Attempts to restrict the concept of evolution to biology are gratuitous."[2]

Descent with modification. E.O. Wilson defines, "evolution is any change in gene frequency in a population." This is narrower than the first definition because it just includes biological change, and only those changes which are inherited.

Universal common ancestor. This is the idea that there is some last universal common ancestor, from which all plants, animals, fungi, and other life on Earth are directly descended.

When evolution is defined simply as "the gradual appearance of new forms of life" over geological time, then 55% of Americans agree with biologists and geologists that evolution has really occurred. Disagreement on this point comes mainly from Young Earth Creationists.

But when defined more narrowly as new forms of life coming into being "without any intervention from God", only 13% to 16% of Americans agree.

Advocates for the teaching of evolution as a finding of mainstream science tend to use two different meanings of "evolution".

We have fossil evidence for evolution. It's a fact. (teacher in CNN article)

This apparently refers to the assertion that the appearance of new forms of life is supported by fossils (see carbon dating). But the context of the quote implies that the teacher was actually talking about the notion that "new species can evolve from older ones -- such as humans evolving from ancient apes." [1]